For some applications such as adhesives individual polymers do not possess the necessary combination of properties. Individual polyolefins having certain characteristics are often blended together in the hope of combining the positive attributes of the individual components. Typically the result is a blend which displays an average of the individual properties of the individual resins. For example EP 0 527 589 discloses blends of flexible, low molecular weight amorphous polypropylene with higher molecular weight isotactic polypropylene to obtain compositions with balanced mechanical strength and flexibility. These compositions show better flexibility compared to that of the isotactic polypropylene alone, but are still lacking in other physical attributes. Physical blends also have the problems of inadequate miscibility. Unless the components are selected for their compatibility they can phase separate or smaller components can migrate to the surface. Reactor blends, also called intimate blends (a composition comprising two or more polymers made in the same reactor or in a series of reactors) are often used to address these issues, however finding catalyst systems that will operate under the same environments to produce different polymers has been a challenge.
Multiple catalyst systems have been used in the past to produce reactor blends (also called intimate blends) of various polymers and other polymer compositions. Reactor blends and other one-pot polymer compositions are often regarded as superior to physical blends of similar polymers. For example U.S. Pat. No. 6,248,832 discloses a polymer composition produced in the presence of one or more stereospecific metallocene catalyst systems and at least one non-stereospecific metallocene catalyst system. The resultant polymer has advantageous properties over the physical blends disclosed in EP 0 527 589 and U.S. Pat. No. 5,539,056.
Thus there has been interest in the art in developing multiple catalyst systems to produce new polymer compositions. For example, U.S. Pat. No. 5,516,848 discloses the use of two different cyclopentadienyl based transition metal compounds activated with alumoxane or non-coordinating anions. In particular, the examples disclose, among other things, catalyst compounds in combination, such as (Me2Si(Me4C5)(N-c-C12H23)TiCl2 and rac-Me2Si(H4Ind)ZrCl2, or Me2Si(Me4C5)(N-c-C12H23)TiCl2 and Me2Si(Ind2)HfMe2, (Ind=indenyl) activated with activators such as methylalumoxane or N,N-dimethyl anilinium tetrakis(pentafluorphenyl) borate to produce polypropylenes having bimodal molecular weight distributions (Mw/Mn), varying amounts of isotacticity (from 12 to 52 weight % isotactic PP in the product in Ex 2, 3 and 4), and having weight average molecular weights over 100,000, and some even as high as 1,200,000 for use as thermoplastics. Likewise, U.S. Pat. No. 6,184,327 discloses a thermoplastic elastomer comprising a branched olefin polymer having crystalline sidechains and an amorphous backbone wherein at least 90 mole percent of the sidechains are isotactic or syndiotactic polypropylene and at least 80 mole percent of the backbone is atactic polypropylene produced by a process comprising: a) contacting, in solution, at a temperature from about 90° C. to about 120° C., propylene monomers with a catalyst composition comprising a chiral, stereorigid transition metal catalyst compound capable of producing isotactic or syndiotactic polypropylene; b) copolymerizing the product of a) with propylene and, optionally, one or more copolymerizable monomers, in a polymerization reactor using an achiral transition metal catalyst capable of producing atactic polypropylene; and c) recovering a branched olefin polymer. Similarly U.S. Pat. No. 6,147,180 discloses the synthesis of a thermoplastic polymer composition, which is produced by first polymerizing monomers to produce at least 40% vinyl terminated macromonomers and then copolymerizing the macromonomers with ethylene. In addition U.S. Pat. No. 6,323,284 discloses a method to produce thermoplastic compositions (mixtures of crystalline and amorphous polyolefin copolymers) by copolymerizing alpha-olefins and alpha, omega dienes using two separate catalyst systems.
Likewise others have experimented with multiple stage processes to produce new polymer compositions. For example EP 0 366 411 discloses a graft polymer having an EPDM backbone with polypropylene grafted thereto at one or more of the diene monomer sites through, the use of a two-step process using a different Ziegler-Natta catalyst system in each step. This graft polymer is stated to be useful for improving the impact properties in blended polypropylene compositions.
Although each of the polymers described in the above references has interesting combinations of properties, there remains a need for new composition that offer other new and different property balances tailored for a variety of end uses. In particular, it would be desirable to find a composition that is strong yet has adhesive characteristics and the ability to be applied using adhesive technology and equipment.
For general information in this area, one may refer to:
1. DeSouza and Casagrande, in 2001 addressed the issue of binary catalyst systems in “Recent Advances in Olefin Polymerization Using Binary Catalyst Systems, Macromol. Rapid Commun. 2001, 22, No. 16 (pages 1293 to 1301). At page 1299 they report propylene systems that produce a “gooey” product.
2. Studies with respect to the production of stereoblock polypropylene by using in-situ mixtures of metallocene catalysts with different stereoselectivity were recently performed by Lieber and Brintzinger in “Propene Polymerization with Catalyst Mixtures Containing Different Ansa-Zirconocenes: Chain Transfer to Alkylaluminum Cocatalysts and Formation of Stereoblock Polymers”, Macromolecules 2000, 33, No. 25 (pages 9192–9199). Propylene polymerization reactions were performed using metallocene catalysts H4C2(Flu)2ZrCl2, rac-Me2Si(2-Me-4-tBu-C5H2)2ZrCl2 and rac-Me2Si(2-MeInd)2ZrCl2 in the presence of either MAO (methylalumoxane) or triisobutylaluminium (AliBu3)/triphenylcarbenium tetrakis(perfluorophenylborate) (trityl borate) as the cocatalyst. Propylene polymerization using the mixed catalysts, H4C2(Flu)2ZrCl2 and rac-Me2Si(2-MeInd)2ZrCl2 in the presence of either MAO or AliBu3/trityl borate produced waxy solids, which are completely separable into an atactic (diethyl ether-soluble) and an isotactic (insoluble) fraction. Neither fraction contained any combination of isotactic and atactic pentad patterns indicating that these catalyst mixtures did not form stereoblock polymers.
3. Aggarwal addressed the various polymers produced in “Structures and Properties of Block Polymers and Multiphase Polymer Systems: An Overview of Present Status and Future Potential”, S. L. Aggarwal, Sixth Biennial Manchester Polymer Symposium (UMIST Manchester, March 1976)
4. “Selectivity in Propene Polymerization with Metallocene Catalysts” Resconi, et al, Chem Rev. 2000, 100, 1253–1345.
None of the references above has directly addressed the need for polyolefin based adhesives containing both amorphous and crystalline components. Such adhesives are desired in the industry as a replacement for blends requiring significant amount of hydrocarbon resin tackifiers.
Additional references that are of interest include:
1) EP Patents: EP 0 619 325 B1, and EP 719 802 B1;
2) U.S. patents/Publications: U.S. Pat. Nos. 6,207,606, 6,258,903, 6,271,323, 6,340,703, 6,297,301, US 2001/0007896 A1, U.S. Pat. Nos. 6,184,327, 6,225,432, 6,342,574, 6,147,180, 6,114,457, 6,143,846, 5,998,547, 5,696,045; 5,350,817, and 6,659,965.
3) PCT Publications: WO 00/37514, WO 01/81493, WO 98/49229, WO 98/32784; and WO 01/09200
4) “Metallocene-Based Branch-Block thermoplastic Elastomers,” Markel, et al. Macromolecules 2000, Volume 33, No. 23. pgs 8541–8548.